Stop me if you've heard this one:

Patient: "Doctor, doctor, I have a serious problem. You've got to help me. I can't remember anything."

Doctor: "When did you first notice that you had this problem?"

Patient: "What problem?"

Whether or not Jonathan Nolan ever heard that one, his short story illustrates not so much the hokey wit behind the sally but the horror that inhabits the body of a man actually afflicted with this rare disease. In the story adapted and directed by the writer's brother, Christopher Nolan, "Memento" tells of a thirty-something insurance investigator who, in the process of rescuing his wife from a rapist, suffers a blow to his head that causes him short-term memory. He cannot remember facts, names or faces once they are out of his mind for a few minutes, though memories of his life before the encounter with the attacker seem to be no problem for him. Or so he believes. As a memento of each meeting with a man, a woman or even a car, he snaps a Polaroid picture, captioning each shot with a fleeting statement like "Don't believe his lies," and dedicates his life to avenging his wife's rape-murder. Since the thought of revenge compels his every action, he actually tattoos vital information to his body, even having license numbers etched into his thigh and letters across his chest running backward so that they will appear normal when he faces himself in the mirror. Most chilling is the simple announcement written in reverse across his chest, "John G. raped and murdered my wife."

A thinking person's thriller with some occasionally startling albeit split-second sounds and striking imagery, Nolan's movie is an original. The story is told backwards, but this is not a mere gimmick such as that used to no useful effect by Mike Figgis, who divided his screen for "Time Code" into quadrants. Nolan is attempting to put the viewer into the poor guy's mind to show the confusion that has taken over his life, in effect making the audience as flustered as the brain-damaged Leonard--whose role is performed almost as a one-man show by the alarmingly talented Guy Pearce ("L.A. Confidential").

The story begins, then, with the conclusion. Leonard has wrestled a man known as Teddy (Joe Pantoliano) to the ground and has put a gun to Teddy's face prepared to do him in for the murder of his wife. But who, really, is Teddy? Is he the perpetrator against whom Leonard is justifiably seeking revenge? We don't know because Leonard himself doesn't know, a concept that gives the picture its fascinating intrigue. "Memento" is a jigsaw puzzle which, each time you think you have the pieces in place, you are confronted with a new twist that keeps you guessing about each individual's role.

For example, who is the mysterious Natalie (Carrie-Anne Moss), a woman willing to help Leonard gain his revenge? Is she merely using him to gain the satisfaction that she seeks, a vengeance against a man who has beaten her silly? Or does she take pity on this bewildered individual, empathizing with his tragedy and willing to go the distance for the stranger out of sheer compassion? Why does Nolan bring in the character of Sammy (Stephen Tobolowsky), a man who has apparently suffered a similar ailment as Leonard and whom Leonard is investigating to determine whether Sammy's affliction is an insurance-covered physical condition or an insurance exempted psychological one?

Most of all, who is Leonard and why has he been able to afford to drive a Jaguar and wear designer suits on the salary of an insurance investigator? He doesn't know, so we are kept in the dark as well. By the final minutes of the film (that is, the beginning of the action), some but not all of the enigma is resolved. This is not the kind of solution that most people in the audience would have guessed, I would imagine, making "Memento" a satisfying puzzle throughout and, perhaps equally important, a vehicle for 32-year-old Guy Pearce's tour de force performance--which is backed up well by an ensemble which includes Mark Boone Junior as Burt, who manages one of the motels in which Leonard is living anonymously and especially Carrie-Anne Moss (seen in November of 2000 in the far bigger-budgeted but less challenging "Red Planet"). Viewers accustomed to clever indies such as this one already know that you don't need megabucks to challenge and entertain. With the limited budget available to the producers and the circumscribed time afforded to its filming, Nolan's work is probably edgier than it would have been had the intensity and focus been missing.